Methods of making paper tissue, towel, and the like, are well known, including various features such as Yankee drying, through-air drying (TAD), fabric creping, dry creping, wet creping, and so forth. Conventional wet pressing (CWP) processes have certain advantages over conventional through-air drying (TAD) processes including: (1) lower energy costs associated with the mechanical removal of water rather than transpiration drying with hot air; and (2) higher production speeds that are more readily achieved with processes that utilize wet pressing to form a web. On the other hand, through-air drying processes have become the method of choice for new capital investment, particularly for the production of soft, bulky, premium quality towel products.
Fabric creping has been employed in connection with papermaking processes which include mechanical or compactive dewatering of the paper web as a means to influence product properties. See U.S. Pat. Nos. 4,689,119 and 4,551,199 of Weldon; U.S. Pat. No. 4,849,054 of Klowak; and U.S. Pat. No. 6,287,426 of Edwards et al. Operation of fabric creping processes has been hampered by the difficulty of effectively transferring a web of high or intermediate consistency to a dryer. Further U.S. patents relating to fabric creping include the following: U.S. Pat. No. 4,834,838; U.S. Pat. No. 4,482,429 as well as U.S. Pat. No. 4,445,638. Note also, U.S. Pat. No. 6,350,349 to Hermans et al., which discloses wet transfer of a web from a rotating transfer surface to a fabric.
In connection with papermaking processes, fabric molding has also been employed as a means to provide texture and bulk. In this respect, there is seen in U.S. Pat. No. 6,610,173 to Lindsay et al. a method for imprinting a paper web during a wet pressing event which results in asymmetrical protrusions corresponding to the deflection conduits of a deflection member. The '173 patent reports that a differential velocity transfer during a pressing event serves to improve the molding and imprinting of a web with a deflection member. The tissue webs produced are reported as having particular sets of physical and geometrical properties, such as a pattern densified network and a repeating pattern of protrusions having asymmetrical structures. With respect to wet-molding of a web using textured fabrics, see also, the following U.S. Pat. No. 6,017,417 and U.S. Pat. No. 5,672,248 both to Wendt et al.; U.S. Pat. No. 5,505,818 to Hermans et al. and U.S. Pat. No. 4,637,859 to Trokhan. With respect to the use of fabrics used to impart texture to a mostly dry sheet, see U.S. Pat. No. 6,585,855 to Drew et al., as well as United States Publication No. 2003/0000664, now U.S. Pat. No. 6,607,638.
U.S. Pat. No. 5,503,715 to Trokhan et al. discloses a cellulosic fibrous structure having multiple regions distinguished from one another by basis weight. The structure is reported as having an essentially continuous high basis weight network, and discrete regions of low basis weight which circumscribe discrete regions of intermediate basis weight. The cellulosic fibers forming the low basis weight regions may be radially oriented relative to the centers of the regions. The paper may be formed by using a forming belt having zones with different flow resistances. The basis weight of a region of the paper is generally inversely proportional to the flow resistance of the zone of the forming belt, upon which such a region was formed. The zones of different flow resistances provide for selectively draining a liquid carrier having suspended cellulosic fibers through the different zones of the forming belt. A similar structure is reported in U.S. Pat. No. 5,935,381, also to Trokhan et al., where the features are achieved by using different fiber types.
Through-air-dried (TAD), creped products are disclosed in the following patents: U.S. Pat. No. 3,994,771 to Morgan, Jr. et al.; U.S. Pat. No. 4,102,737 to Morton; and U.S. Pat. No. 4,529,480 to Trokhan. The processes described in these patents comprise, very generally, forming a web on a foraminous support, thermally pre-drying the web, applying the web to a Yankee dryer with a nip defined, in part, by an impression fabric, and creping the product from the Yankee dryer. A relatively uniformly permeable web is typically required, making it difficult to employ recycle furnish at levels that may be desired. Transfer to the Yankee typically takes place at web consistencies of from about 60% to about 70%.
As noted above, through-air-dried products tend to exhibit enhanced bulk and softness; however, thermal dewatering with hot air tends to be energy intensive and requires a relatively uniformly permeable substrate. Thus, wet-press operations wherein the webs are mechanically dewatered are preferable from an energy perspective and are more readily applied to furnishes containing recycle fiber, which tends to form webs with less uniform permeability than virgin fiber. A Yankee dryer can be more effectively employed because a web is transferred thereto at consistencies of 30% or so, which enables the web to be firmly adhered for drying.
Despite the many advances in the art, improvements in absorbent sheet qualities such as bulk, softness and tensile strength generally involve compromising one property in order to gain an advantage in another. Moreover, existing premium products generally use limited amounts of recycle fiber or none at all, despite the fact that use of recycle fiber is beneficial to the environment and is much less expensive as compared with virgin kraft fiber.